Accurate, tunable optical synthesis has potential applications in standoff effluent characterization, high-bandwidth and secure communications, optical spectroscopy, gas sensing, LiDAR, optical-carrier atomic clocks, and atomic and optomechanical inertial sensors. Current state-of-the-art optical synthesizers are limited to laboratory use due to the size, cost, and power requirements.
Optical synthesizers that achieve accurate and stable optical output over a wide range (such as the C-band optical communications range of 1530-1565 nm), have output light that is locked to a highly stable and accurate optical reference with feedback control in the radio frequency (RF) domain. For large scale optical synthesizers, self-referenced optical frequency combs based on titanium-sapphire or fiber-laser based femtosecond mode-locked laser sources are used to reference optical output to microwave inputs, enabling optical synthesis. These devices are available commercially, are as large as a refrigerator, and use large amounts of power.
Significant efforts have been taken in the last few years to develop self-referenced optical frequency combs based on micro-resonators, which use much less power to operate than the tradition mode-locked laser based optical frequency combs. However, optical frequency combs operate by self-referencing in an optical interferometer. This has not been achieved using micro-resonators because of an inability to control micro-resonators with fine comb tooth spacing while simultaneously being excited with laser power in excess of 1 watt, which is used to create combs wide enough (e.g., octave spanning) to self-reference.